The prior art, and anyone skilled in the art, is already aware of hydraulic systems of various arrangements of hydraulic pumps and driving engines and valves for directing hydraulic-flow to a load-supporting member, such as a hydraulic cylinder or a hydraulic motor or the like. In previously known hydraulic systems, the hydraulic pump or pumps are employed for working upon the workload in whatever manner rquired, and the driving engine is relied upon for producing sufficient power to drive the pumps to support whatever load the system may be designed to support. However, it is common knowledge that the systems can be overloaded to an extent that the engine can no longer drive the pumps, and thus the engine will falter and even stall, and then the entire tractor, vehicle, or whatever system is employed, will become completely inoperative.
The present invention provides an arrangement for avoiding the aforementioned problem of stalling the driving engine. In accomplishing this objective, the present invention provides a hydraulic system wherein one of two or more hydraulic pumps can be unloaded, depending upon the condition of the hydraulic pressure and flow in the system, that is, depending upon the force exerted by the system to support and move a workload. Still further, the present invention accomplishes the unloading in an automatic manner, that is without requiring manual control of valves, and the system is also arranged so that it automatically becomes reset and self-operating when the hydraulic condition within the system regains its normal condition subsequent to one of the pumps being automatically unloaded, as mentioned.
Still further, the aforementioned objectives are also accomplished in conditions where the hydraulic fluid is cold, and thus the aforementioned objectives are accomplished for a cold-start type of condition and therefore one of two or more pumps is automatically unloaded and retained unloaded until the hydraulic fluid reaches an effective working temperature.
Still further, the hydraulic system of this invention accomplishes the aforementioned objectives in a system which is designed and arranged according to the stall speed of the engine. That is, the load which is supported by the system is related to the power producible by the engine so that when the maximum load is exceeded, the system will automatically unload itself and avoid stalling the driving engine. Additionally, the entire hydraulic system is not unloaded at the point just prior to engine stall speed, but only a part of the system is unloaded, to avoid engine stall, but another part of the system remains effective and operative to support the workload or to perform its work.
Still further, it is an object of this invention to provide a hydraulic pump or automatic unloading system which is both hydraulic speed and hydraulic pressure sensitive for effecting the automatic unloading of a part of the hydraulic drive system, while leaving the remainder of the hydraulic drive system operative for supporting a workload.
Other objects and advantages will become apparent upon reading the following description in light of the accompanying drawings.